The Salt of the Earth - Ocean Worlds: The Story of Seas on Earth and Other Planets - page 69

in their gold teeth; trace amounts of the metal were even present in
the glassware and the reagents they were using. When one is trying to
measure minuscule amounts of something, then even tiny amounts
of contamination can ratchet up the errors by orders of magnitude.
Slipshod practice by scientists who should have known better? These
were early days, we must remember. Rather, it was progress in ana-
lytical precision, painfully attained.
Of other substances in seawater, some are a little surprising, taking
our 30 kilograms or so of sodium chloride and one hundredth of a mil-
ligram of gold, per tonne, as measured on a scale of abundance. Take
iron for instance. It is abundant in the Earth's crust and a major com-
ponent of many of the common rock-forming minerals. In seawater
there is a mere 3 milligrams per tonne—something that has had pro-
found effects, and seen profound changes, in time and space within the
Earth's oceans, as we will see later in this chapter and in Chapter 6.
There is more molybdenum (about 1 gram per tonne) and rubidium
(more than 10 grams per tonne) dissolved in the waters of the sea—
although less aluminium (about 1 milligram per tonne).
And so we can go on, running through the elements—even those
present in smaller amounts than gold. There are quite a few here: rhe-
nium, osmium, ytterbium, thorium, and more. The saltiness of the
sea, indeed, has almost infinite variety. What is a little surprising, per-
haps even disconcerting, is that the chemistry of the sea now bears
little resemblance to the chemistry that is being washed in by rivers.
There is a mismatch here, and that does demand explanation.
The Salt Supply
Water, one may repeat, is a marvellous solvent. As it travels its powers
of dissolution may, indeed, increase. Drifting in the atmosphere as
fine cloud droplets and falling through the air as raindrops, it absorbs
carbon dioxide, sulphur dioxide, nitrogen dioxide, and other gases